WASHINGTON — To wage war in Yemen, Saudi Arabia is using F-15 fighter jets bought from Boeing. Pilots from the United Arab Emirates are flying Lockheed Martin’s F-16 to bomb both Yemen and Syria. Soon, the Emirates are expected to complete a deal with General Atomics for a fleet of Predator drones to run spying missions in their neighborhood.

As the Middle East descends into proxy wars, sectarian conflicts and battles against terrorist networks, countries in the region that have stockpiled American military hardware are now actually using it and wanting more. The result is a boom for American defense contractors looking for foreign business in an era of shrinking Pentagon budgets — but also the prospect of a dangerous new arms race in a region where the map of alliances has been sharply redrawn.

Last week, defense industry officials told Congress that they were expecting within days a request from Arab allies fighting the Islamic State — Saudi Arabia, the Emirates, Qatar, Bahrain, Jordan and Egypt — to buy thousands of American-made missiles, bombs and other weapons, replenishing an arsenal that has been depleted over the past year.

The United States has long put restrictions on the types of weapons that American defense firms can sell to Arab nations, meant to ensure that Israel keeps a military advantage against its traditional adversaries in the region. But because Israel and the Arab states are now in a de facto alliance against Iran, the Obama administration has been far more willing to allow the sale of advanced weapons in the Persian Gulf, with few public objections from Israel.

“When you look at it, Israel’s strategic calculation is a simple one,” said Anthony H. Cordesman of the Center for Strategic and International Studies. The gulf countries “do not represent a meaningful threat” to Israel, he said. “They do represent a meaningful counterbalance to Iran.”

Industry analysts and Middle East experts say that the region’s turmoil, and the determination of the wealthy Sunni nations to battle Shiite Iran for regional supremacy, will lead to a surge in new orders for the defense industry’s latest, most high-tech hardware.

The militaries of gulf nations have been “a combination of something between symbols of deterrence and national flying clubs,” said Richard L. Aboulafia, a defense analyst at the Teal Group. “Now they’re suddenly being used.”

Saudi Arabia spent more than $80 billion on weaponry last year — the most ever, and more than either France or Britain — and has become the world’s fourth-largest defense market, according to figures released last week by the Stockholm International Peace Research Institute, which tracks global military spending. The Emirates spent nearly $23 billion last year, more than three times what they spent in 2006.

Qatar, another gulf country with bulging coffers and a desire to assert its influence around the Middle East, is on a shopping spree. Last year, Qatar signed an $11 billion deal with the Pentagon to purchase Apache attack helicopters and Patriot and Javelin air-defense systems. Now the tiny nation is hoping to make a large purchase of Boeing F-15 fighters to replace its aging fleet of French Mirage jets. Qatari officials are expected to present the Obama administration with a wish list of advanced weapons before they come to Washington next month for meetings with other gulf nations.

American defense firms are following the money. Boeing opened an office in Doha, Qatar, in 2011, and Lockheed Martin set up an office there this year. Lockheed created a division in 2013 devoted solely to foreign military sales, and the company’s chief executive, Marillyn Hewson, has said that Lockheed needs to increase foreign business — with a goal of global arms sales’ becoming 25 percent to 30 percent of its revenue — in part to offset the shrinking of the Pentagon budget after the post-Sept. 11 boom.

American intelligence agencies believe that the proxy wars in the Middle East could last for years, which will make countries in the region even more eager for the F-35 fighter jet, considered to be the jewel of America’s future arsenal of weapons. The plane, the world’s most expensive weapons project, has stealth capabilities and has been marketed heavily to European and Asian allies. It has not yet been peddled to Arab allies because of concerns about preserving Israel’s military edge.

But with the balance of power in the Middle East in flux, several defense analysts said that could change. Russia is a major arms supplier to Iran, and a decision by President Vladimir V. Putin to sell an advanced air defense system to Iran could increase demand for the F-35, which is likely to have the ability to penetrate Russian-made defenses.

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“This could be the precipitating event: the emerging Sunni-Shia civil war coupled with the sale of advanced Russian air defense systems to Iran,” Mr. Aboulafia said. “If anything is going to result in F-35 clearance to the gulf states, this is the combination of events.”

At the same time, giving the gulf states the ability to strike Iran at a time of their choosing might be the last thing the United States wants. There are already questions about how judicious Washington’s allies are in using American weaponry.

“A good number of the American arms that have been used in Yemen by the Saudis have been used against civilian populations,” said Daryl Kimball, executive director of the Arms Control Association, an assertion that Saudi Arabia denies.

Mr. Kimball said he viewed the increase in arms sales to the region “with a great deal of trepidation, as it is leading to an escalation in the type and number and sophistication in the weaponry in these countries.”

Congress enacted a law in 2008 requiring that arms sales allow Israel to maintain a “qualitative military edge” in the region. All sales to the Middle East are evaluated based on how they will affect Israeli military superiority. But the Obama administration has also viewed improving the militaries of select Arab nations — those that see Iran as a threat in the region — as critical to Israeli security.

“It is also important to note that our close relationships with countries in the region are critical to regional stability and Israel’s security,” Andrew J. Shapiro said in a speech in 2011, when he was an assistant secretary of state for political-military affairs. “Our relationships with Egypt, Jordan, Lebanon and many Gulf countries allow the United States to strongly advocate for peace and stability in the region.”

There is an unquestionably sectarian character to the current conflicts in the Middle East, nowhere more so than in the Saudi-led air campaign in Yemen. The Saudis have assembled a group of Sunni nations to attack Houthi militia fighters who have taken over Yemen’s capital, Sana, and ousted a government backed by Saudi Arabia and the United States. Saudi officials have said that the Houthis, a Shiite group, are being covertly backed by Iran. Other nations that have joined the coalition against the Houthis, like Morocco, have characterized their participation in blunt sectarian terms.

“It’s a question of protecting the Sunnis,” Mbarka Bouaida, Morocco’s deputy foreign minister, said in an interview.

But Sunni nations have also shown a new determination to use military force against radical Sunni groups like the Islamic State. A number of Arab countries are using an air base in Jordan to launch attacks against Islamic State fighters in Syria. Separately, the Emirates and Egypt have carried out airstrikes in Libya against Sunni militias there.

Meanwhile, the deal to sell Predator drones to the Emirates is nearing final approval. The drones will be unarmed, but they will be equipped with lasers to allow them to better identify targets on the ground.

If the sale goes through, it will be the first time that the drones will go to an American ally outside of NATO.

A version of this article appears in print on April 19, 2015, on Page A1 of the New York edition with the headline: Sale of U.S. Arms Fuels the Wars of Arab States. Order Reprints|Today's Paper|Subscribe